The Centers for Disease Control estimates that half of more than 100 million annual prescriptions of antibiotics are unnecessary. As a result, microbes have, in many cases, adapted and are resistant to antibiotics due to constant exposure and improper use of the drugs. It is estimated that the annual cost of treating drug resistant infections in the United States is approximately $5 billion. This continued emergence of anti-microbial-resistant bacteria, fungi, yeast and parasites has encouraged efforts to develop other agents capable of killing pathogenic microbes. Furthermore, there are urgent needs for target-specific anti-microbial agents since many microbial pathogens reside with non-harmful commensal bacteria that are important for the health of the human host.
Recent scientific studies have revealed a class of naturally occurring anti-microbial peptides in humans, other mammals, plants, insects and other organisms. A negative aspect of treatment with antibiotics or anti-microbial peptides is their indiscriminate killing or inhibition of a broad spectrum of microorganisms. The human body is home to millions of different bacteria, many of which are vital for optimal health. Overuse of broad-spectrum antibiotics can seriously disrupt the ecology of the normal human microbiota rendering humans more susceptible to bacterial, yeast, viral, and parasitic infections. This effect is also seen with administration of anti-microbial peptides. For example, the antibiotic peptide histatin kills most gram-positive bacteria in the oral cavity. Thus general administration of histatin can lead to undesirable effects by allowing the overgrowth of gram-negative bacteria, such as Actinobacillus sp or Fusobacterium sp, many of which may cause periodontal diseases. Accordingly, histatin is not useful by itself for prevention of dental caries.
Another disadvantage of administration of anti-microbial peptides is their ability to damage host cells at higher concentrations since these positively charged peptides can also penetrate and disrupt eukaryotic cell membranes.
Previous efforts to deliver of pharmaceutically active agents to specific targets relied principally on chemically conjugating a pharmaceutically active agent to a targeting component. For example Shih et al. U.S. Pat. No. 5,057,313 refers to targeting delivery of drugs, toxins and chelators to specific sites in an organism by loading a therapeutic or diagnostic component onto a polymeric carrier, followed by conjugation of the carrier to a targeting antibody. Hansen, U.S. Pat. No. 5,851,527 claims a similar invention.
A drawback to this approach is that the non-specific linkage of the pharmaceutical reagents to unknown sites on the antibody molecule used for targeting may interfere with delivery of the therapeutic agents. See Rodwell et al., U.S. Pat. No. 4,671,958. Moreover, chemical modification of a targeting antibody by the nonspecific reactions during conjugation may substantively alter the antibody itself, thereby affecting its binding to targets. Furthermore, chemical linkage is very inefficient and the result is non-uniform, making the technique very difficult to use in practice.
More recently, there have been a number of reports of the use of recombinant techniques to produce fusion proteins for the treatment of disease. See Penichet and Morrison, J. Immunological Methods, 248:91-101 (2001) for review. Penichet et al. discuss efforts to treat malignant disease using a genetically engineered protein construct including an immunological component that binds specifically to tumor cells and a cytokine capable of eliciting significant antitumor activity. See, e.g. Pastan et al. U.S. Pat. No. 5,981,726, and Fell, Jr. et al., U.S. Pat. No. 5,645,835.
However, to date there have not been any reports of directing anti-microbial agents to infected regions of humans or animals using target-specific molecules. There is a need in the art to provide methods and compositions useful for treatment of microbial organisms and microbially mediated diseases, especially microbial diseases of mucosal surfaces that are not readily accessible by normal anti-microbial mechanisms provided by the immune system.